Help:Introduction to Categories

Categories are an way to tag articles in a way which makes them accessible and well-arranged. To see a list of existing categories, click here.

Organization

To avoid needing to tag an article with many categories, we are attempting to organize them in a hierarchy, and only tagging articles with the most localized category. (It is possible to tag an article with more than one category, if that is appropriate.) That will automatically make them available through the higher-level categories as well.

For instance, the category Category:Operating Systems contains the sub-category Category:DEC Operating Systems, which then contains the sub-sub-categories Category:PDP-10 Operating Systems, Category:PDP-11 Operating Systems, etc. Tagging an article with just the latter automatically enables it to be found via any of the larger categories.

Some articles may need to be placed higher in the hierarchy than others, if there is no appropriate sub-category; e.g. Multics has to go in the top-level category Category:Operating Systems since it was sui generis.

Syntax

To add an article to a category, simply put [[Category:Category name]] in an article. (Convention dictates that this be at the bottom of the article, but it could in princible be anywhere). This creates the category if it did not already exist.

However, since a new category is empty of any descriptive text, it will still appear as a red link until there is text in the category's page (which you can edit as you would a regular article).

To arrange a sub-category of a category, simply edit the sub-category's page to place the sub-category in the parent category, just as you would to place an article in a category. The sub-category will automatically be placed in the parent category.

To link to a category without placing the article in this category, prepend a colon to the link, as so: [[:Category:Category name]].